Actuator for a valve, in particular a turbine valve

ABSTRACT

An actuator includes a valve spindle, for adjustment of an opening position for a valve and a drive piece for the valve spindle. The drive piece is connected to the valve spindle, by a storage device, which may be pre-tensioned to a particular pre-tensioned value during a pre-tension process, in such a manner that, with a pre-tensioned storage device the opening position can be set without altering the value of the pre-tensioning. The actuator is particularly suitable for a valve on a steam turbine or a gas turbine. As an example, the actuator may be a hydraulic damping unit, integrated in a damping piston. The damping unit permits a reliable end-travel damping for the valve, in particular in the case of rapid closure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to GermanApplication Nos. 00122837.8 filed on Oct. 20, 2000 and 01119339.8 filedon Aug. 10, 2001, the contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an actuator for a valve, in particular aturbine valve, with a valve spindle for setting an opening position ofthe valve and with a drive part assigned to the valve spindle.

2. Description of the Related Art

A turbine, in particular a steam turbine, normally has a considerablenumber of valves which may be used, for example, as fresh-steam,interception or diversion valves and as quick-action stop valves. Theopening position of each of these valves serves in this case for settinga respective material, gas or steam stream and can be set, for example,via a valve spindle assigned to the respective valve. Such a valvespindle is an integral part of an actuator assigned to the valve. Theactuator may in this case have to satisfy very high requirements,particularly in terms of actuating force and actuating speed. For a highreliability of the valve, it may be necessary, for example, for theactuator to have an actuating force of about 200 kN and an actuatingtime of about 100 ms, particularly when there is a quick-action stoprequirement.

The valves are therefore conventionally designed as oil-hydraulicallyoperated actuating valves, the actuators assigned to them including ineach case an oil-hydraulic device. For operating the actuators andtherefore the valves, for example, a central hydraulic supply system maybe provided. For a central hydraulic supply system of this type,however, it is necessary to have a complex and therefore cost-extensivepipeline system which should also be designed redundantly for highoperating reliability. To simplify a complex supply system of this type,European patent application EP 0 040 732 A1 and the paper by W.Kindermann, E. G. Egener and H. Tremühlen, “Compact Valve ActuatorControl System for Large Steam Turbines”, presented at the AmericanPower Conference, Chicago, 1984, disclose actuators for steam turbinevalves which in each case have a decentralized hydraulic system. Thehydraulic system of an actuator of this type is integrated into acompact drive block arranged on a valve housing, so that only a cablesystem is still necessary in order to supply energy to the actuator. Byoil being used as hydraulic fluid, an ignition of the oil and thereforea fire in the steam turbine could occur under extremely unfavorablecircumstances. Admittedly, with a view to fire protection,low-combustible fluids may also be used as hydraulic fluid. However,low-combustible hydraulic fluids of this type are costly and, because oftheir lower stability, as compared with hydraulic fluids based onmineral oils, require comparatively complicated care measures.

DE-A-1 937 198 describes a regulating valve for regulating the pressureand/or the quantity of a flowing medium in power stations, chemicalplants or the like. The regulating valve has a push rod, to which avalve seat is fastened. The push rod is coupled to an electricservo-motor via a beam rotatable about a central center of rotation. Thequantity of medium flowing through the valve can thereby be set.Furthermore, a return spring engages on the push rod.

EP 0 230 849 A1 specifies a regulating valve and a shut-off valve. Thevalve has a shut-off body which is displaceable along an axis and whichhas a piston extending along the axis. The piston is designed as aspur-toothed rack which is in contact with a longitudinal toothing of afurther bar. As a result of a rotation of this further bar about its baraxis, a displacement of the shut-off body in the axial direction can beachieved. A rotation of this bar takes place by a further toothing atthe end of this bar via an electric motor.

DE 44 46 605 A1 discloses a valve for a steam turbine which has a valvespindle with a valve cone arranged on it. The valve spindle is drivenvia an electric motor which is connected to the valve spindle via anelectromagnetically actuated coupling. For automatic self-closing of thevalve, the latter includes a cup-spring system. The electromagneticcoupling is connected to a threaded bush which cooperates with a valvespindle guided fixedly in terms of rotation and which thus moves thelatter axially. The threaded bush is designed as a ball-screw bush, sothat it acts upon the valve spindle with low play and low friction.Since the valve spindle is guided fixedly in terms of rotation, that isto say it can only be moved up and down axially when the threaded bushrotates, it is not necessary to have a drive which has the effect oftranslational motion. Instead, an electric motor rotating in twodirections is sufficient for this purpose. However, the electric motormust have a torque safeguard, in order thereby to ensure that, forexample during the closing of the valve, the valve cone adjoining thevalve spindle at one end is not damaged or does not damage the sealingseat (valve seat) assigned to the valve cone when the latter comes tobear on the sealing seat.

WO 98/13633 specifies an actuator for a valve for a turbine, the openingposition of which valve can be set by a push rod, a fault-free operationof the valve being ensured, along with a particularly low fire risk. Forthis purpose, an electric motor is provided for driving the push rod.The push rod is connected to the electric motor via a gearwheel/racksystem and via an electromagnetic toothed coupling. For reasons ofoperating reliability for the actuator and therefore also for the valvecapable of being driven by the latter, in WO 98/13633 a retaining-springsystem is also arranged on the push rod. The system includes a retainingspring which is arranged in a housing and which acts on a thrust platefastened to the push rod. The actuator is in this case designed in sucha way that the spring force of the retaining spring causes a closing ofthe valve. In this case, for opening the valve, the electric motor actscounter to the spring force of the retaining spring.

An electromechanical actuator for a valve, in particular for a steamturbine valve, is specified in WO 99/49250. The actuator has a push rodand an electric motor for driving the push rod. The push rod and theelectric motor are connected via a transmission device, by which achanging torque can be generated, depending on the axial displacement ofthe push rod. The push rod is connected to a return-spring system. Inthis case, even in the closing position of the valve, the push rod isloaded by the return force of the return-spring system which is designedas a valve cup spring accumulator assembly. During an opening movementof the actuator, the return-spring system is further tensioned andreaches its maximum return force when the valve is in the open position.Consequently, in a similar way to what is described in WO 98/13633,during the setting of an opening position of the valve, the drive has toperform work counter to the considerable return force of thereturn-spring system.

SUMMARY OF THE INVENTION

An object on which the invention is based is, therefore, to specify animproved actuator for a valve, in particular for a turbine valve, inwhich, along with a particularly low fire risk, a fault-free andreliable operation of the valve is ensured and the setting of an openingposition of the valve is possible with little effort.

This object is achieved, according to the invention, by an actuator fora valve, in particular a turbine valve, with a valve spindle for settingan opening position of the valve and with a drive part assigned to thevalve spindle, the drive part being coupled to the valve spindle via anaccumulator device pretensionable to a pretension in a tensioningoperation, in such a way that, with the accumulator device pretensioned,the pretension remains unchanged during the setting of the openingposition.

The invention is based on the knowledge that, in conventional actuatorswhich are equipped with a safety quick-action stop system, the settingof an opening position of a valve by an actuator coupled to the valve ispossible only with considerable effort. This is because work has to beperformed with respect to the return force of a spring, for example avalve cup spring accumulator assembly. During an opening movement of theactuator, the spring is tensioned and reaches its maximum return forcewhen the valve is in the opening position. This requires a correspondingheavy-duty design of the drive part driving the valve spindle. Owing tothis type of rigid coupling of the setting operation and the operationof tensioning the spring for the quick-action stop system, in the eventof a regular change or setting of the opening position of the valve agenerally very high changing force always has to be applied to the valvespindle. The necessary setting force in this case increasescontinuously, for example, during opening and decreases continuously,according to the spring characteristic, during closing. In addition,when an opening position is held, for example with the valve fully open,the (maximum) return force has to be maintained by additional measures.The drive parts of valves of this type and the coupling, gear and motorcomponents connected to a drive part have a correspondingly complexdesign.

By contrast, the actuator of the invention opens up a completely new wayof making it possible to set an opening position of a valve assigned tothe actuator, while at the same time having high operating reliability.Proceeding from the above-described disadvantages in the knownembodiments, the fundamental idea of the proposed actuator lies in aseparation and therefore uncoupling of the operation of setting anopening position from the operation of tensioning the accumulatordevice. The drive part is coupled to the valve spindle via anaccumulator device pretensionable to a pretension in a tensioningoperation, in such a way that, with the accumulator device pretensioned,the pretension remains unchanged during the setting of the openingposition. The pretensioning of the accumulator device and the setting ofthe opening position of the valve are therefore conceived as independentoperations which do not influence one another. Thus, for example, withthe valve fully closed, the accumulator device can be pretensioned to apretension, and, the thereafter, an opening position of the valve can beexecuted by the drive part assigned to the valve spindle, without anyfurther action on the accumulator state of the accumulator device.

Advantageously, as a result, the effort for setting an opening positioncan be reduced considerably. In particular, during a setting operation,the setting force is essentially constant due to the uncoupling from thetensioning operation. The drive part and further drive components, forexample a gear and/or a motor, assigned, if appropriate, to the drivepart can be designed specially with a view to the requirements duringthe setting operation. To be precise, by virtue of the uncoupling of thetensioning operation and the setting operation, a controlled adaptationand design of the drive part and, if appropriate, of further drivecomponents according to the respective operation can advantageously beachieved for the first time. This may be implemented, for example, by atwo-stage design of the drive part with a power stage for the tensioningoperation and with a now generally substantially lower power stage forthe setting operation.

In this case, in a preferred embodiment of the invention, during thesetting of the opening position, the actuating force to be applied forthis purpose is lower than the pretension. The effort involved in asetting operation is thereby reduced considerably, with the result thatthe mechanical load on the components, for example valve spindle ordrive part, which move during a setting operation is correspondinglyreduced. The wear of these components and of the components coupled, ifappropriate, to them is thereby likewise markedly lower, with a resultthat the useful life of the actuator and a valve connected to theactuator is increased correspondingly. Advantageously, due to thereduced effort involved in setting an opening position, acorrespondingly larger number of setting operations, as compared withthe known embodiments of an actuator, can be achieved.

In a further preferred embodiment, the drive part is connected underpretension to the accumulator device in such a way that the drive partis moved jointly with the accumulator device during the setting of theopening position. By virtue of this embodiment, advantageously, theaccumulator device is moved jointly with the drive part. Since the drivepart drives the valve spindle during the setting of the openingposition, the movement of the valve spindle is thus also synchronizedwith the movement of the accumulator device. Advantageously, thisresults in a comprehensive availability of the accumulator device,particularly of the pretension stored in the accumulator device, in allthe phases of a setting operation. Thus, in the event of a necessaryquick-action closure of the valve, the pretension stored in theaccumulator device is available at any time and immediately for thequick-action closure. Due to the synchronization of the movement duringthe setting of an opening position, the accumulator device as a whole ismoved, the pretension remaining unchanged.

Preferably, to maintain the pretension, a latching element which latchesduring the tensioning operation is provided. During a tensioningoperation, the accumulator device is pretensioned to a pretension. Inthis case, a corresponding potential energy is stored in the accumulatordevice. The latching element ensures that the stored energy ismaintained and is available at any time, for example, for a quick-actionclosure. In this case, if necessary, the latching element can bereleased in a short time and therefore the potential energy stored inthe accumulator device can be freed and used for a quick-action closure.The main task of the latching element is, however, to preserve theenergy stored in the accumulator device for a long period of time, sothat reliable operation during the setting of the opening position isensured. Advantageously, moreover, the energy content in the accumulatordevice can be predetermined by the exact configuration and arrangementof the latching element. In this case, with an appropriatelypredeterminable pretension, a latching position of the latching elementcan be determined and, in structural terms, provided for the tensioningoperation.

Preferably, the latched latching element holds at least about 50% of thepretension. Advantageously, in this case, the latching element holds aslarge a fraction of the pretension of the accumulator device aspossible. Preferably, the latching element holds the entire pretensionof the accumulator device, so that the entire stored potential energy inthe accumulator device, at the same time as being held by the latchingelement, is also secured. The exact selection of the fraction of thepretension held by the accumulator device can in this case be adapted tothe respective structural conditions and to the quick-action closurerequirements relevant for use.

In a particularly preferred embodiment, a release device is provided,which holds approximately up to 50% of the pretension. By a releasedevice being provided, in combination with the latching element, aparticularly effective storage and release of the pretension energystored in the accumulator device is achieved. In this case,advantageously, the essential fraction of the pretension is held by thelatching element, while the release device holds a correspondinglysmaller fraction of the pretension.

Advantageously, via the release device, the potential energy stored inthe accumulator device can be released, for example, as a function of arelease criterion. The release device may in this case be designed aspart of the latching element or else be conceived independently of this.Advantageously, therefore, for example, a quick-action closure of avalve connected to the actuator can be triggered by the release device.In this case, the release device releases that fraction of storedpretension which is held by it, and the released energy can be used fortriggering an operation for the detensioning of the entire accumulatordevice. Consequently, for example, the latching element can be released,the latching element being released from its latching position. This mayadvantageously take place solely by virtue of the controlledproportionate distribution of the pretension to be held to the latchingelement and to the release device, in that, for example, the latchingelement is designed with a view to a predeterminable maximum tolerablepretension. When this maximum value is exceeded, the latching element isreleased and the pretension stored in the accumulator device is releasedessentially completely within a short time.

Advantageously, owing to the proportionate distribution of thepretension which is to be held by the latching element and the releasedevice, a particularly flexible adaptation to the respective structuralconfiguration of the latching element and of the release device ispossible. In general, in this case, the latching element will hold theessential fraction of the pretension and the release device only asmaller fraction in order to trigger a release. It is a particularadvantage in this case, that, by a skillful distribution of thefractions to the latching elements and the release device, a releasecriterion can be set in a flexible way:

Preferably, the release device can be activated electromagnetically, inparticular by a coil. In this case, with a change in an electromagneticflux, the release device releases the pretension in the accumulatordevice. A change in an electromagnetic flux may in this case signify aconnection or alternatively also a disconnection of an electromagneticfield. This can be implemented, in particular, by a coil which, with therelease device closed, that is to say with the pretension of theaccumulator device being held, can be operated with current load oralternately also currentlessly. The release device can be activated indifferent ways, as required, by a corresponding change in anelectromagnetic flux.

In a particularly preferred embodiment, the latching element has apliable, in particular resiliently elastic, tongue for positiveengagement with a latching ramp. During the tensioning operation, thetongue of the latching element comes into contact with the latchingramp, the tongue being moved in relation to the latching ramp. Owing tothe pliable, in particular resiliently elastic, design of the tongue,particularly effective contact can be made between the tongue and thelatching ramp, a force being applied. For this purpose, the latchingramp may have a contact surface which forms, for example, an inclinedplane in relation to the tongue of the latching element. Thus, during atensioning operation, the tongue slides upward along the inclined planeand, after the end of the tensioning operation, latches into a latchingposition, a positive connection being made between the latching ramp andthe pliable tongue. In this case, advantageously, the latching ramp maybe designed as part of the drive part, during a tensioning operation,the drive part which has the latching ramp being moved with respect tothe latching element which has the tongue. After the tensioningoperation, positive engagement is achieved, the latching elementdwelling, together with the tongue, in the latching position, theaccumulator device of the actuator being acted upon by correspondingpretension. The pliable tongue may in this case be formed of an elasticmaterial, for example of a metal. During the setting of the openingposition of the valve after a tensioning operation, the pretension ofthe accumulator device remains unchanged.

Preferably, a plurality of tongues are provided, which bracket thelatching ramp in a circumferential direction. A multiple securing of thelatching element by a corresponding multiplicity of tongues can therebybe achieved. Furthermore, the bracketing in a circumferential directionensures a uniform latching and holding of the pretension, whileadvantageously, during the tensioning operation, circumferentialguidance is achieved during the relative movement between the tonguesand the latching ramp, in a similar way, for example, to a bush whichguides a shaft. A tensioning operation can thus be achieved reproduciblyand uniformly, while avoiding mechanical stress peaks in an individualtongue or in a region of the contact surface between a tongue and thelatching ramp. The plurality of tongues is in this case advantageouslyarranged essentially concentrically around a drive part having alatching ramp. By an additionally symmetric arrangement of the tongues,a particularly uniform load absorption and load distribution are ensuredduring a tensioning operation, in particular during the positivelatching or engagement of the tongues with the latching ramp. Moreover,by virtue of this symmetric arrangement of the tongues, a particularlyuniform pretensioning of the accumulator device can be achieved, highreliability being afforded by this type of guidance.

In a further preferred embodiment, a bracket basket partially formed bythe tongues is provided, the bracket basket bracketing the drive part.In the case of a plurality of tongues which are each designed, forexample, as a pliable, in particular resiliently elastic, metal strip ormetal lamellae, these form the open end of the bracket basket orlamellar basket. The bracket basket brackets the drive part, while, as aresult of the pliably elastic properties of the tongues, a bracket forceacting over the full circumference perpendicularly to the contactsurface between the bracket basket and the drive part is exerted on thedrive part.

As a result of this bracket action, the bracket basket or lamellarbasket is connected to the drive part in a particularly advantageousway. Insofar as the drive part has at the same time a latching ramp, abracket force also acts during a tensioning operation and, inparticular, in the latching position. During a tensioning operation, thebracket basket partially formed by the tongues is moved in relation tothe latching ramp, particularly in relation to the drive part, at thesame time a pretension being applied to the accumulator device.

The bracket basket or lamellar basket in this case preferably may beformed of an elastic material, for example a metal sheet, which isappropriately machined (for example, punched) and shaped in order toproduce the tongues or lamellae.

Preferably, a spring element, in particular a cup spring, storing thepretension is arranged in the bracket basket. A system formed of cupsprings, for example what is known as a cup spring assembly, may also beprovided in the bracket basket or lamellar basket. By a spring elementbeing arranged in the bracket basket, the spring element is enclosed bythe bracket basket both during a tensioning operation and during thesetting of an opening position of the valve. Thus, after a tensioningoperation, the pretension stored in the spring element is as it werealso enclosed. The enclosure or bracketing can be changed in such a waythat, in the event of a release, for example by the above-describedrelease device, the enclosed pretension, that is to say the spring forcestored in the spring element, loosens or else releases the bracketing,and the spring element can thereby expand within a short time. Thereleased spring energy is in this case used conventionally for anoperation for the quick-action closure of a valve connected to theactuator. In this case, the valve spindle is brought in a short timefrom an opening position into the closing position by the expandingspring element. Before a (regular) setting of an open position of thevalve is carried out, the spring element is to be pretensioned anew, forexample for reasons of operating reliability, the valve preferablydwelling in its closing position. After the tensioning operation, asetting of an opening positon of the valve by the pretension springelement enclosed in the bracket basket can take place without any changein the pretension of the spring element. In particular, there is no needfor any effort with respect to the return force of the spring element,in order to achieve the desired opening position of the valve spindle,since the tensioning operation is uncoupled from the setting operation,that is to say from the setting of an opening position.

Preferably, the bottom of the bracket basket has a damper piston whichis provided for damping the movement of the valve spindle, in particularduring an expansion of the spring element. By the damper piston,end-position damping, for example during a quick-action closure of thevalve, that is to say during an acceleration of the valve spindle froman opening position into the closing position, is achieved, but, forexample, also whenever an end position is reached after the setting ofan opening position.

Advantageously, in this case, the damper piston is an integral part ofthe bracket basket or lamellar basket, so that the bracket basketthereby performs a double function, to be precise the reception of thepretensioned spring element and the property of ensuring the desiredend-position damping in the event of a quick-action closure. The damperpiston may in this case be capable of being pushed in and consequentlyof being guided in a damping cylinder which is assigned to the damperpiston and which may also be designated as the main damping cylinder,the damping cylinder being additionally acted upon, for damping, by adamping fluid or hydraulic fluid, for example oil.

Further particularly preferred embodiments of a markedly improveddamping can be achieved by the measures described in detail below:

In a particularly preferred embodiment, the hydraulic damping device forend-position damping is integrated to the damper piston.

In the present design of the actuator with a drive part which is coupledto the valve spindle via an accumulator device pretensionable to apretension in a tensioning operation, for example via anelectromechanical coupling, a virtually rigid connection or coupling isafforded between the drive part and the valve spindle and a valve coneor closing piece adjoining the latter. If the drive part is separatedfrom the valve spindle in the event of quick-action closure triggering,the energy, now acting freely, of the accumulator device, for example apretensioned cup spring system, accelerates the valve spindle togetherwith the following valve cone in the closing direction. In this case,closing speeds of typically 4 m/s or above are customary. In the rangeof opening of about 10 to 20%, it is therefore beneficial to providehydraulic damping which reduces the closing speed to, for example, 0.5m/s, so that an impact of the valve spindle or of the following valvecone into the valve seat, with possible accompanying damage, can belargely ruled out. The integrated hydraulic damping device proves to beparticularly advantageous in this case for end-position damping. Thisend-position damping, at the moment when the valve spindle with a valvecone is set down into the valve seat, cancels the rigid coupling betweenvalve spindle and spring element, and the kinetic energy is reducedconsiderably. In this case, by virtue of the integrated design, aparticularly compact construction is additionally implemented. Incooperation with a damping cylinder, the damper piston, together withthe integrated hydraulic damping device, allows a particularly reliableand durable operation of the actuator precisely in quick-action closuresituations.

In a particularly preferred embodiment, the hydraulic damping deviceincludes a first sealing space and a second sealing space different fromthe first sealing space, in this case hydraulic fluid, for example oil,for damping being capable of being supplied to or of being dischargedfrom the sealing spaces of a function of the opening position.

In this case, preferably, the supply or discharge of a hydraulic fluidin the first sealing space and in the second sealing space is broughtabout in each case via a differential pressure induced as a result of achange in volume of the sealing spaces. Thus, an integrated dampingdevice controlled by differential pressure is provided, which, dependingon the opening position, ensures particularly adapted damping. Dependingon whether the pressure in a sealing space is higher or lower than theambient pressure, such as corresponds, for example, to the pressure ofthe hydraulic fluid which is located in an interspace formed by thedamper piston together with a damping device and a damping cylindersurrounding the damper piston, a positive or negative differentialpressure will be obtained with respect to the sealing space underconsideration. As a result, hydraulic fluid is correspondingly suppliedto the sealing space or discharged, in particular pressed, out of thesealing space.

To use a change in volume of sealing space in order to build up thedifferential pressure proves in this case to be particularlyadvantageous, because a change in volume can be achieved during anactuating operation in a relatively simple way as a function of therespective opening position of the actuator.

For the spatial separation of the first sealing space from the secondsealing space, a movable actuator plate is preferably provided. Thesealing spaces are thereby separated spatially from one another, forexample the first sealing space being arranged in the direction of theclosing position and the second sealing space in the direction of theopening position of the actuator. The movable actuator plateadvantageously at the same time assumes a further function, in that iteffects a change in volume of a sealing space. For this purpose, theactuator plate may be indirectly or directly connected to the valvespindle or coupled to the latter.

In a preferred embodiment, a hydraulic throttle element is adjacent toat least one of the sealing spaces. An outflow of hydraulic fluid fromthe respective sealing space is thus possible advantageously only oressentially only via this throttle element. In this case, the timeprofile of the outflow of hydraulic fluid, for example of oil, can bepredetermined via the cross section of the throttle element. The oilflowing out of the throttle can be received in a largely pressurelesscollecting space formed, for example, within the housing of theactuator.

In a further preferred embodiment, one sealing space has arranged in ita deformable sealing element, via the deformation of which the volume ofthe sealing space can be changed. Depending on the actuating operationand actuating situation, particularly as a function of the direction ofmovement of the valve spindle, the deformable sealing element isdeformed and in the process, for example, compressed or stretched.

Consequently, the sealing surface assigned to the sealing element iscorrespondingly increased or reduced. This change in the effectivesealing surface via a deformation of the sealing element has a directeffect on a change in volume of the sealing space under consideration.The sealing space is correspondingly reduced or increased. What can thusbe achieved, in cooperation with the movable actuator plate, is that theother sealing space in each case behaves in the opposite way to thesealing space under consideration and either increases its volumecorrespondingly, that is to say, as a result, the sealing space isfilled with hydraulic fluid owing to the vacuum which builds up, or elsethe volume is correspondingly reduced, this being accompanied by adischarge of oil from the sealing space. In this advantageousembodiment, a respective sealing element is provided, for example, onboth sides of the actuator plate, a first deformable sealing elementbeing assigned to the first sealing space and a second deformablesealing element being assigned to the second sealing space.

Preferably, a setting element, in particular a setscrew, is provided,which acts directly or indirectly on the sealing element and serves forsetting the elasticity of the sealing element. The setting element mayin this case, for example, pretension the deformable sealing element,thus changing the elastic properties of the sealing element. Theachievable change in volume in the sealing spaces and the differentialpressure brought about thereby can consequently be set, thuscorrespondingly influencing the damping properties of the integratedhydraulic damping device.

Advantageously, the actuator is characterized by a design for a valve ofa steam turbine. Further applications of the actuator for valves inother turbomachines, for example in a gas turbine, are likewisepossible. In view of the requirements placed on a valve to be designedto be acted upon by fresh steam under high pressure of up to 300 bar andhigh temperatures of up to 650° C. and on a corresponding actuator, theactuator according to the present invention appears to be particularlysuitable for use in a steam turbine valve, in particular for the feed offresh steam.

However, the fundamental idea of the concept according to the inventioncan also readily be applied to actuators for valves in other technicalsectors, for example as a fitting in plants of the chemical industry orin pipelines carrying a hot pressure-loaded fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more apparent and more readily appreciated from the followingdescription of an exemplary embodiment, taken in conjunction with theaccompanying drawings which are partially diagrammatic and not true toscale and, for the sake of clarity and for understanding, cover only thecomponents of an actuator which are important for the explanation. Inthe drawing:

FIGS. 1 to 4 show in each case a longitudinal section through adiagrammatically illustrated actuator in various actuating states,

FIG. 5 shows a sectional view of the actuator illustrated in FIG. 4along the sectional line V—V perpendicular to the longitudinal axis 37,

FIG. 6 shows a sectional view, similar to FIG. 5, of the actuator asshown in FIG. 4, with an alternative embodiment of the bracket basket,

FIG. 7 shows a view of the detail VII of the actuator shown in FIG. 2,with a hydraulic damping device integrated into the damper piston,

FIGS. 8 and 9 show in each case the detail VII of the actuator as shownin FIG. 3, with the accumulator device pretensioned during the settingof an opening position, with an integrated hydraulic damping device,

FIG. 10 shows, in a detailed view according to the detail X of FIG. 4,the integrated hydraulic damping device after the triggering of aquick-action closure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference symbols refer to like elementsthroughout.

FIG. 1 shows, in longitudinal section, an actuator 1 for a valve, inparticular a turbine valve. The actuator extends along a longitudinalaxis 37 and has, successively along the axis 37, a valve spindle 3 forsetting an opening position of a valve, not illustrated in any moredetail in FIG. 1, an accumulator device 7 and a drive part 5. The drivepart 5, the accumulator device 7 and the valve spindle 3 are in thiscase arranged at least partially in a housing 29. The accumulator device7 has a spring element 21, the spring element 21 being composed of amultiplicity of cup springs 23A, 23B arranged along the longitudinalaxis 37 and adjacent to one another. The drive part 5 is coupled to thevalve spindle 3 via the accumulator device 7. The coupling of theaccumulator device 7 to the valve spindle 3 is achieved via a damperpiston 27 formed at the bottom 25 of the accumulator device 7. For thispurpose, the valve spindle 3 is connected to the damper piston 27. Thedamper piston 27 limits the accumulator device 7 in an axial directionalong the longitudinal axis 37. At that end of the accumulator device 7which is located opposite the damper piston 27 along the longitudinalaxis 37, the accumulator device 7 has a latching element 9. The latchingelement 9 has a tongue 15 which extends in a direction parallel to thelongitudinal axis 37. The tongue 15 in this case may be formed of apliable, in particular resiliently elastic material, for example ametal. The drive part 5 of the actuator 1 is contiguous to the latchingelement 9 of the accumulator device 7 along the longitudinal axis 37.The coupling of the accumulator device 7 to the drive part 5 takes placeby contact of the tongue 15 with an outer surface 45 of the drive part5. Further coupling of the drive part 5 to the accumulator device 7takes place by contact via a thrust surface 47 of the spring element 21.The thrust surface 47 is in this case in contact with the outer surface45 of a ram 49 of the drive part 5, the ram extending along thelongitudinal axis 37. Thus, as required, for example during a tensioningoperation, a force F can be exerted on the spring element 21 in thedirection of the longitudinal axis 37 via the thrust surface 47. Thedrive part 5 has a latching ramp 17 which is formed on the outer surface45 over the circumference of the drive part 5. In this case, thelatching element 9 of the latching ramp 17 are contiguous to oneanother, the latching element 9 following the latching ramp 17 in thedirection of force, as seen in the direction of the force F to beapplied. The latching element 9 bears with the tongue 15 on the outersurface 45 of the latching ramp 17, a positive connection beingachieved. The drive part 5 has, further, a release device 11 whichincludes a coil 13. The coil 13, in this case, can be acted upon by anelectrical current and is integrated into the drive part 5.Nonintegrated embodiments, with a release device 11 arranged separatelyfrom the drive part 5, are likewise possible.

A damping cylinder 31 is adjacent to the damper piston 27 along thelongitudinal axis 37, the damping cylinder 31 surrounding the damperpiston 27 so as to form a gap 51. The damper piston 27 is in an abutmentor end position along the longitudinal axis 37 with respect to thedirection of a force F to be applied. The valve spindle 3 connected tothe damper piston 27 is consequently in a closing position 53, a closingpiece (valve cone), not shown in FIG. 1, connected to the valve spindle3 being seated sealingly in a valve seat of a valve, likewise notillustrated in FIG. 1, connected to the actuator 1. As a result of theclosing position 53 of the valve spindle 3, a fluid fed to a turbinewith the aid of a valve assigned to the valve spindle 3 is interruptedin its flow. Consequently, with the valve closed, no fluid, for examplehot steam for a steam turbine, is fed. In the actuating state of theactuator 1, as shown in FIG. 1, the spring element 21 is largelyexpanded. This actuating state, with the valve closed and theaccumulator device 7 expanded, may occur, for example, after aquick-action closure of the actuator 1 and of the associated valve hastaken place.

After a quick-action closure has taken place, in order to set an openingposition of the valve, first the accumulator device 7 is to bepretensioned with a predeterminable pretension. The operation of tensionin the accumulator device 7 is illustrated in more detail in FIG. 2which shows the actuator 1 of FIG. 1 in an actuating state during anoperation for tensioning the accumulator device 7. In a tensioningoperation, a pretension is applied to the spring element 21 of theaccumulator device 7, in that a force F, provided via the drive part 5,is exerted on the thrust surface 47 of the spring element 21. The springelement 21 or the cup springs 23A, 23B forming the spring element 21 arethereby compressed. At the same time, the ram 49 is moved parallel tothe longitudinal axis 37 in the direction of the force F. An elasticbending apart or opening of the tongue 15 of the latching element 9 isassociated with this deflection of the drive part 5 with respect to thestationary accumulator device 7, the tongue 15 remaining in contact withthe latching ramp 17 during this relative movement and followingessentially the contour of the latching ramp 17 during the linearmovement. The latching ramp 17 has a contour with a rising flank 33 andwith a falling flank 35 adjoining the rising flank 33 along thelongitudinal axis 37. The surface 45 forms, along the rising flank 33and the falling flank 35, a reaction surface for the latching element 9,in particular for the pliable, resiliently elastic tongue 15. Inaddition to a tongue 15, the latching element 9 may also have a furthertongue 15A, both the tongue 15 and the further tongue 15A sliding alongthe latching ramp 17 during the tensioning operation, at the same timebeing spread apart in a plane perpendicular to the longitudinal axis 37.When a force F growing according to the spring characteristic of thespring element 21 is exerted further, the tensioning operation iscontinued until the tongue 15, 15A, gradually closing together again,slides along the falling flank 35 of the latching ramp 17 and finallythe latching element 9 latches into place the latter reaching itslatching position. When the latching position is ultimately reached (seealso FIG. 3), the tensioning operation is concluded and the accumulatordevice 7 is pretensioned to a pretension Fv. At the same time, theactuator 1 is brought into an actuating state which representsoperational readiness for setting an opening position D of a valveconnected to the actuator 1 (operating position). In the latchingposition, the latching element 9, together with the pliable, resilientlyelastic tongue 15, 15A, is in positive engagement with the latching ramp17. The latching element 9 is thus latched, the tongue 15, 15A fittingsnugly against the release device 11.

The functioning of the actuator 1 in the operating position, that is tosay with the accumulator device 7 pretensioned with a pretension Fv, isexplained in more detail in FIG. 3. In the operating position, thepretensioned spring element 21 is enclosed between the bottom 25 of thedamper piston 27 and the ram 49 of the drive part 5. The release device11 is activated, in that an electrical current flows through themagnetic coil 13. When a material which is magnetic at least in regionsis used for the tongue 15, 15A, the tongue 15, 15A is attracted and heldby the activated magnet coil 13. In this state, the stored spring energy21 of the accumulator device 7 is enclosed, the tongues 15, 15Abracketing the latching ramp 17 in a circumferential direction. In thecase of an appropriate multiplicity of tongues, 15, 15A (cf., forexample, FIGS. 5 and 6), a bracket basket 19 or lamellar basket 19formed partially by the tongues 15, 15A is thereby provided, the bracketbasket 19 bracketing the drive part 5. The spring element 21 storing thepretension Fv is arranged in the bracket basket 19. The drive part 5 iscoupled to the valve spindle 3 via an accumulator device 7 pretensionedto the pretension Fv in the tensioning operation, in such a way that,with the accumulator device 7 pretensioned, during the setting of anopening position D, the pretension Fv remains unchanged. As comparedwith the closing position 53, the actuator 1 shown in FIG. 3 is in anopening position D, the damper piston 27 being deflected completely outof the damping cylinder 31 along the longitudinal axis 37. To set orchange the opening position D, an actuating force Fs, Fs′ is necessary,which is provided by the drive part 5 and is transmitted to theaccumulator device 7 and the valve spindle 3 connected to the latter. Byan actuating force Fs along the longitudinal axis 37 in a directionfacing away from the damping cylinder 31, an increase in the openingposition D is achieved. By an actuating force Fs′ in an oppositedirection to the actuating force Fs, that is to say along thelongitudinal axis 37 in a direction facing the damping cylinder 31, theopening position D is reduced. Thus, by the opening position D beingset, the throughflow through a valve capable of being operated by theactuator 1 can be set exactly.

The accumulator device 7 is in this case connected to the drive part 5in such a way that, under the pretension Fv, the drive part 5 is movedjointly with the accumulator device 7 during the setting of the openingposition D. Since the valve spindle 3 is connected to the damper piston27 of the accumulator device 7, the valve spindle 3 follows the actuatorforce Fs, Fs′ provided by the drive part 5. During the setting of theopening position D, the actuating force Fs, Fs′ to be applied for thispurpose is lower than the pretension Fv. The setting of an openingposition D can thus take place with a considerably lower actuating forceFs, Fs′ than in conventional actuators. In particular, by the conceptaccording to the invention, the tensioning operation for pretensioningthe accumulator device 7 is separated from the actual setting of anopening position D, so that the tensioning operation and the settingoperation are independent of one another. During the setting of theopening position D, the pretension Fv of the pretensioned accumulatordevice 7 remains unchanged, whereas, in conventional actuators with aspring accumulator, work has to be performed counter to the return forcein order to set an opening position D. An opening position D may in thiscase also coincide with the closing position 53, so that D is then equalto 0.

For reasons of operating reliability of the actuator 1 and thereforealso for a valve capable of being driven by the actuator 1, inparticular for a steam turbine valve, the drive part 5 is coupled to thevalve spindle 3 via the accumulator device 7 pretensioned to apretension Fv in the tensioning operation. The accumulator device 7includes the spring element 21, the abovementioned spring element 21being arranged in the bracket basket 19 and acting on the damper piston27 fastened to the valve spindle 3, the pretension F_(v) acting, inparticular, on the bottom 25 of the damper piston 27. The actuator 1 isin this case designed in such a way that the spring force of the springelement 21 can, if necessary, bring about a rapid closing of the valvecapable of being driven by the actuator 1. In a closing operation ofthis type, the damper piston 27 together with a valve spindle 3 isaccelerated by the expanding spring element 21 and is brought into theclosing position 53. This quick-action closing operation, as it isknown, is triggered in that the release device 11 releases the tongue15, 15A. For this purpose, the current flow through the magnet coil 13of the release device 11 is disconnected. As a result of the release,owing to the pretension F_(v), the latching element 9 is released fromthe latching ramp 17 and, together with the entire bracket basket 19, isaccelerated in the direction of the closing position 53. In the event ofa current failure and of an associated undersupply of the magnet coil13, an automatic self-closing of the actuator 1 and of the valve capableof being driven by the latter is thus ensured (cf. FIG. 4).

FIG. 4 illustrates an actuating state of the actuator 1 after anautomatic self-closure. This actuating state essentially correspondsagain to the actuator state, shown in FIG. 1, of the actuator 1 with theaccumulator device 7 expanded, in particular with an expanded springelement 21. As a result of the quick-action closure, the valve spindle 3is in the closing position 53 and a valve, not illustrated in FIG. 4,assigned to the actuator 1 is closed. To set an opening position D, theaccumulator device 7 is first to be pretensioned anew with a pretensionFv, in that a force F is to be applied, parallel to the longitudinalaxis 37, to the drive part 5. The more detailed particulars of atensioning operation are already discussed exhaustively in connectionwith FIG. 1.

To improve the damping properties in a quick-action closure, the gap 51formed by the damper piston 27 and the damping cylinder 31 may be actedupon at least partially by a damping fluid 55. The damping fluid 55 isin this case, for example, the hydraulic oil which serves at the sametime for lubricating the movable components arranged in the housing 29of the actuator 1. In addition, the valve spindle 3 is sealed off withrespect to the damping cylinder 31 and to the housing 29 by respectivesealing element 41, 39. The sealing elements 39, 41 prevent an outflowof damping fluid 55 from the gap 51 and from the housing 29.Furthermore, the sealing elements 39, 41 bring about a guidance of thevalve spindle 3, so that the latter can be set uniformly andreproducibly into an opening position D or, if necessary, for example ina quick-action closure, can be brought into the closing position. To setan opening position D, further drive components, not illustrated in theFIGURES, may be connected to the drive part 5. These may be, forexample, a gear and an electric motor driving the gear. In this case,the electric motor delivers the torque which actuates the drive part 5,designed, for example, as a ball-screw drive, via a, for example,multistep gear, for example an angular gear. The rotational movement ofan electric motor is consequently converted into a linear movement ofthe drive part 5. By an electric motor being provided, together with theactuator 1, an electromechanical actuator is provided for a valve.However, in addition to the ball-screw drive mentioned by way ofexample, other drives, for example with a crank disk or an eccentricdisk, may also come under consideration in order to set the drive part 5in a linear movement. The concept of the invention can consequently beadapted to different gear forms in a highly flexible way. Furthermore,the actuator 1 is suitable in a highly advantageous way for differentvalves. It may be used for steam turbine valves, gas turbine valves orfittings in industrial plants, for example in the chemical industry,where a reliable and accurate operation of the actuator 1 is to beensured.

In order to illustrate alternative embodiments of the bracket basket 19,FIGS. 5 and 6 show in each case a sectional view along the sectionalline V—V of the actuator 1 illustrated in FIG. 4. The section is in thiscase to be understood as being perpendicular to the longitudinal axis37, as a result of which a sectional plane with a first axis 57 and witha second axis 59 extending perpendicularly to the first axis 57 isdefined. In FIG. 5, four tongues 15, 15A, 15B, 15C are provided, whichbracket the drive part 5. The tongues 15, 15A are in this case arrangedalong the first axis 57, while the tongues 15C, 15B are arranged alongthe second axis 59. In this case, the tongue 15 lies opposite the tongue15A and the tongue 15C lies opposite the tongue 15B along the respectiveaxis 57, 59, the drive part 5 being bracketed. Each of the tongues 15,15A, 15B, 15C is in this case in contact with the outer surface 45 ofthe drive part 5 and exerts a bracketing force or clamping force on theouter surface 45.

An alternative embodiment with a plurality of tongues 15, 15A, 15B, 15C,15D, 15E, 15F, 15G is shown in FIG. 6. The tongues 15A, 15B, 15C, 15D,15E, 15F, 15G are in this case arranged concentrically around the drivepart 5 symmetrically in a circumferential direction. By virtue of thesymmetrical arrangement, a particularly uniform force distribution andload absorption can be achieved, with the result that, in a tensioningoperation, the latching element 9 having the tongues 15, 15A, 15B, 15C,15D, 15E, 15F, 15G comes into engagement with the latching ramp 17particularly effectively. Furthermore, in a tensioning operation, thebracket basket 19 is guided particularly uniformly in its movement inrelation to the drive part 5, in particular to the ramp 49 and thelatching ramp 17.

FIG. 7 illustrates in more detail the detail VII of FIG. 2, which showsan operation for tensioning the accumulator device. In the tensioningoperation, a pretension is applied to the spring element 21 of theaccumulator device 7 (cf. FIG. 2). As illustrated in the view of thedetail in FIG. 7, a hydraulic damping device 61 is integrated into thedamper piston 27 for particularly effective end-position damping. Thehydraulic damping device 61 has a first sealing space 63A and a secondsealing space 63B different from the first sealing space 63A. In eachcase a hydraulic fluid 65, for example oil, for damping can be suppliedto the first sealing space 63A and the second sealing space 63B or canbe discharged from the sealing spaces 63A, 63B. For the spatialseparation of the first sealing space 63A from the second sealing space63B, a movable actuator plate 67 is provided. The latter is firmlyconnected to the valve spindle 3, so that a movement of the valvespindle leads directly to the movement of the actuator plate 67. Asealing element 71A is provided in the first sealing space 63A and asealing element 71B is provided in the second sealing space 63B. Thesealing elements 71A, 71B are deformable, that is to say they have someelastic properties, and may be produced, for example, as Viton O-rings.Thus, in the event of a movement of the movable actuator plate 67, asealing element 71A, 71B can be deformed, depending on the direction ofmovement. The deformation of a sealing element 71A, 71B brings about achange in volume of a sealing space 63A, 63B. The supply or discharge ofhydraulic fluid 65 in the first sealing space 63A and/or in the secondsealing space 63B is brought about in each case via a differentialpressure induced as a result of a change in volume in the sealing spaces63A, 63B. A differential pressure is in this case established betweenthe sealing space 63A, 63B under consideration in each case and anambient pressure. The ambient pressure in this case prevails, forexample, within the housing 29, a pressure gradient being established inthe first sealing space 63A via the sealing tip 41. The second sealingspace 63B is delimited by a throttle element 69, via the dimensioning ofwhich, in particular the cross-sectional area of which, an inflow oroutflow of hydraulic fluid 65 into the second sealing space 63B or outof the second sealing space 63B can be exactly defined in time.Furthermore, the damping device 61 has a setting element 73 which may beproduced, for example, in the form of a setscrew. A particulardeformation of the sealing elements 71A, 71B can be preset via thesetting element 73, with the result that the elasticity of the sealingelements 71A, 71B and therefore the damping properties are influenced.The movable actuator plate 67 is arranged, centered approximately in themiddle, within the damper piston 27 and is seated on both sidespositively between the deformable sealing elements 71A, 71B.

As a result of this configuration, a deformable sealing element 71A, 71Bis deformed on one side, depending on the linear direction of movementof the valve spindle. In the case of a compression of the sealingelement 71B, as shown in FIG. 7, the effective sealing surface of thelatter is increased and the first sealing space 73B is reducedcorrespondingly in its effective volume available to the hydraulicfluid. On the opposite side of the movable actuator plate 67, thesealing element 71A, for example a Viton O-ring, comes loose from theactuator plate 67 during the setting operation shown. The first sealingspace 63A assigned to the sealing element 71A is increasedcorrespondingly and is filled with hydraulic fluid 65 by virtue of thedifferential pressure which is established, here a vacuum in the firstsealing space 63A. The deformation of the deformable or elastic sealingelements 71A, 71B is limited by a contact of the sealing elements 71A,71B with the damper piston 27. The damper piston 27 as it were surroundsthe integrated damping device 61, in particular the actuator plate 67,and also the deformable sealing elements 71A, 71B arranged on both sidesof the actuator plate 67 and assigned to a respective sealing space 63A,63B.

FIG. 7 shows in this case the setting situation where the accumulatordevice 7 is pretensioned to a pretension Fv and the valve in the closingposition (cf. also the discussion relating to FIG. 2). In general, inapplication in a steam turbine valve, the latter is designed instructural terms in such a way that the prevailing steam pressure keepsthe valve closed.

In comparison with this, FIGS. 8 and 9 show in each case situationsduring an opening operation of the actuator 1. With reference to FIG. 3which shows such an actuating operation, FIG. 8 shows the start of anopening operation of the actuator 1. The actuator 1 in this caseoperates counter to a sealing force which keeps the valve closed. Thismay be, for example in application in a steam turbine, the sealing forcewhich is provided by the steam pressure, since the steam pressureprevails at a valve cone, not illustrated in any more detail in FIG. 8,which is assigned to the valve spindle 3. As a result of this mechanicalwork of the actuator 1 counter to the sealing force, the damper piston27 comes into contact with the sealing element 71A, which is located inthe first sealing space 63 a. The damper piston 27 in this case deformsthe sealing element 71A, until the damper piston 27 and the movableactuator plate 67 come into contact, that is to say come to bear. At thesame time, the sealing element 71B located in the second sealing space63B is relieved and no longer seals off the second sealing space 63B,since the sealing element 71B comes loose from the movable actuatorplate 67. This leads to an increase in the volume of the second sealingspace 63B. This increase in volume in the second sealing space 63B givesrise to a vacuum, that is to say a differential pressure in relation tothe surroundings, which causes the second sealing space 63B to be filledfurther with hydraulic fluid 65.

FIG. 9 shows, in the detail VIII, an actuating state of the actuator 1,such as arises essentially from the illustration shown in FIG. 3. FIG. 9consequently shows, in the detail, an opening position of a valve, inwhich the actuator 1 has deflected the valve spindle 3, together with adamper piston 27, out of the damping cylinder 31 in the direction of thelongitudinal axis 37. The integrated hydraulic damping device 61 isconsequently likewise deflected correspondingly along the longitudinalaxis 37 together with the damping piston 27. During the actuatingoperation, that is to say during the deflection, the valve spindle 3,together with the movable actuator plate 67 connected to the valvespindle 3, is essentially positively held, and at the same time guided,via the deformable, in particular elastic, sealing elements 71A, 71B. Inaddition, further sealing elements 39, 41, which are designed as sealingtips and via which the valve spindle 3 is sealed and guided, areprovided. Consequently, during an opening operation, such as isillustrated in FIG. 9, both the sealing element 71A arranged in thefirst sealing space 63A and the sealing element 71B, arranged on theopposite side of the actuator plate 67, in the second sealing space 63Bare in a position in contact with the actuator plate 67 and with adelimiting surface, formed by the damper piston 27, of a sealing space63A, 63B. The two sealing elements 71A, 71B are thus pretensioned undera particular elastic tension in the respective sealing space 63A, 63Band are clamped by the actuator plate 67 and the inner delimitingsurface formed by the damper piston 27. The actuator plate 67 is in thiscase not in contact with the damper piston 27, but is essentiallyalready held centrally by the deformable sealing elements 71A, 71B. Thisconfiguration advantageously has the effect that vibrations which mayoccur and which, when the actuator 1 is used in a steam turbine, arepossibly excited by a steam flow through the partially open valve andare transmitted to the actuator 1, in particular the damper piston 27together with the integrated damping device 61, are damped by thesealing spaces 63A, 63B being filled with hydraulic fluid 65, forexample hydraulic oil, and by virtual elastic sealing elements 71A, 71B.

FIG. 10 refers to the detail X of FIG. 4. In this case, an actuatingstate of the actuator 1 after an automatic self-closure or quick-actionclosure is illustrated. This actuating state also again correspondsessentially to the actuating state, shown in FIG. 1 and alreadydiscussed exhaustively, of the actuator 1, with the accumulator device 7expanded, in particular with an expanded spring element 21. As a resultof the quick-action closure, the valve spindle 3 is in the closingposition 53 (cf. FIG. 4), and a valve, not illustrated in more detail inFIGS. 4 and 10, which is assigned to the actuator 1 is closed. Duringthe quick-action closure, the damper piston 27 is accelerated in theclosing direction along the longitudinal axis 37 by the releasedpotential energy of the spring element 21.

As a result of the inertia of the masses accelerated in this case, inparticular the masses of the valve spindle 3 together with the adjoiningvalve cone, not illustrated in any more detail, and the actuator plate67, the sealing element 71 b facing away from the closing position alongthe longitudinal axis 37 is deformed in the second sealing space 63B.The deformation is in this case brought about by a clamping of thesealing element 71B between the actuator plate 67 and a delimitingsurface delimiting the second sealing space 63B and formed by the damperpiston 27. By contrast, in the actuating state depicted in FIG. 10, thesealing element 71A in the first sealing space 63A is essentiallytension-free, that is to say without corresponding deformation. Thedeformation of the sealing element 71B in the second sealing space 63Bdirectly entails a reduction in the effective volume in the secondsealing space 63B. This results in a displacement of hydraulic fluid 65out of the second sealing space 63B. However, as indicated approximatelyvia the corresponding arrows in FIG. 10, the hydraulic fluid 65 canleave the second sealing space 63B via the hydraulic throttle element 69only. When the valve spindle 3 has finally reached the closing position53 (cf. FIG. 4) during the quick-action closure, the mass inertia of thedamper piston 27 and of the spring element 21, by virtue of theirkinetic energy, initially still causes a further deformation of thesealing element 71B in the second sealing space 63B. This deformationafter the valve spindle 3 has reached the closing position 53 is stillcontinued until the damper piston 27 and the actuator plate 67 come intocontact. Up to this contact, hydraulic fluid 65 will further flow out ofthe second sealing space 63B via the hydraulic throttle element 69. Thedimensioning of the hydraulic throttle element 69, particularly in termsof the geometric cross section of the throttle element 69, in this casedetermines the time profile of this fluid outflow and therefore theend-position damping behavior for the damping device 61 in thisoperating state. The hydraulic fluid 65 flowing out of the secondsealing space 63B through the hydraulic throttle element 69 is receivedby an essentially pressureless collecting space, not specifiable in anymore detail, which is delimited, for example, by the housing 29.Consequently, in the case of a triggering of a quick-action closure, amarkedly improved end-position damping for the actuator 1 is achieved bythe damping device 1 integrated into the damper piston 27. As described,the damping device will make it possible, in particular, to have acontrolled reduction in the impact energy when the closing position 53is reached.

The invention has been described in detail with particular reference topreferred embodiments thereof and examples, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention.

1. An actuator for a turbine valve, comprising: a valve spindle to setan opening position of the turbine valve; an accumulator devicepretensionable to a pretension in a tensioning operation; a drive part,coupled to the valve spindle via the accumulator device, to keep thepretension unchanged during setting of the opening position after theaccumulator device has been pretensioned; and a latching element whichlatches during the tensioning operation to maintain the pretension. 2.The actuator as claimed in claim 1, wherein an actuating force appliedfor setting of the opening position is lower than the pretension.
 3. Theactuator as claimed in claim 1, wherein the drive part is moved jointlywith the accumulator device during the setting of the opening position.4. The actuator as claimed in claim 1, wherein the latching elementholds at least approximately 50% of the pretension when latched.
 5. Theactuator as claimed in claim 4, further comprising a release device tohold up to approximately 50% of the pretension.
 6. The actuator asclaimed in claim 5, further comprising a coil to activate said releasedevice electromagnetically.
 7. The actuator as claimed in claim 6,wherein the drive part includes a latching ramp, and wherein thelatching element has a resiliently elastic pliable tongue for positiveengagement with the latching ramp.
 8. The actuator as claimed in claim7, further comprising a plurality of tongues bracketing the latchingramp in a circumferential direction.
 9. The actuator as claimed in claim8, further comprising a bracket basket formed partially by the tongues,the bracket basket bracketing the drive part.
 10. The actuator asclaimed in claim 9, further comprising a cup spring, arranged in thebracket basket, to store the pretension.
 11. The actuator as claimed inclaim 10, further comprising a damper piston at a bottom of the bracketbasket to damp movement of the valve spindle during an expansion of thecup spring.
 12. The actuator as claimed in claim 11, further comprisinga hydraulic damping device for end-position damping, integrated into thedamper piston.
 13. The actuator as claimed in claim 12, wherein thehydraulic damping device includes a first sealing space and a secondsealing space different from the first sealing space; and hydraulic oilfor damping that is one of supplied to and discharged from the first andsecond sealing spaces as a function of the opening position.
 14. Theactuator as claimed in claim 13, wherein one of supply and discharge ofhydraulic fluid in the first and second sealing space is brought aboutvia a differential pressure induced as a result of a change in volume ofthe sealing spaces.
 15. The actuator as claimed in claim 14, wherein thehydraulic damping device further includes a movable actuator plate forspatial separation of the first and second sealing spaces.
 16. Theactuator as claimed in claim 15, wherein the hydraulic damping deviceincludes a hydraulic throttle element adjacent to at least one of thefirst and second sealing spaces.
 17. The actuator as claimed in claim16, wherein arranged in at least one of the first and second sealingspaces is a deformable sealing element to change a volume of the atleast one of the first and second sealing spaces via deformation of thedeformable sealing element.
 18. The actuator as claimed in claim 17,further comprising a setscrew interacting with the deformable sealingelement to set elasticity of the deformable sealing element.
 19. Theactuator as claimed in claim 18, wherein the turbine valve is connectedto a steam turbine.